this invention is directed to a method of determining the effectiveness against microbial growth of certain antimicrobial agents, either alone or as an ingredient of various cosmetic and pharmaceutical products. More particularly, an "in vitro" test method has been devised which is capable of demonstrating the efficacy of an antimicrobial agent in a cosmetic or deodorant product.
The test method of the invention mirrors "in vivo" efficacy and conditions, and provides an indication of how well and for how long an antimicrobial agent is effective in a given product during use. In addition, the test method simulates (i) the dilution effect when the skin is subjected to sweat and microbial attack, and (ii) the diffusion effect of an antimicrobial agent away from the skin as a function of time.
cosmetic products are particularly vulnerable to contamination by microorganisms, and therefore the control of microbial contamination in cosmetic products is an important aspect of cosmetic manufacturing. Cosmetic products provide a good medium for the growth of various kinds of microorganisms, for such products contain water, oils, gums, protein, polyols, and other nutrients which promote growth.
The presence of viable organisms in cosmetic products can cause separation of emulsions, discoloration, and the formation of unpleasant odors. Decomposition of some of the ingredients of a cosmetic product may lead to skin irritation, and the presence of pathogenic organisms can place the user at the risk of infection.
One safeguard use din the pharmaceutical and cosmetic industry has been to evaluate substances intended for the topical application to human skin, for their propensity to irritate and or sensitize the skin. Traditionally, it has been demonstrated that a product can be safely applied to human skin without significant risk of adverse reaction by "Repeated Insult Patch Testing". This "in vivo" procedure is a predictive patch study that can detect weak sensitizers that require multiple applications in order to induce a cell-mediated immune response sufficient to cause an allergic reaction.
Such "in vivo" procedures are costly and time consuming, and must be administered by qualified and specialized personnel who have been trained in the nuances of the test techniques. Typically, for example, these tests involve the use of a study group of hundreds of volunteer subjects, who are under Federal regulations, required to execute an informed consent document prior to entering the study. The study can extend over about a six week period or more, and involves three phases which are termed an Induction Phase, a Test Phase, and a Challenge Phase.
The Induction Phase involves multiple applications of the topical study product to a test site by means of occlusive and semi-occlusive adhesive patches, and evaluation of the test site prior to reapplication to a site. The Rest Phase can be for two weeks or more. The Challenge Phase involves the application of identical patches to sites previously unexposed to the topical study product. If evidence of sensitization such as erythema is shown by response grading, a Rechallenge Phase is added to the test, in which occlusive and semi-occlusive patches are once more applied to naive test sites, in about 1-2 weeks or more following the Challenge Phase.
Another way that the cosmetic industry evaluates the effectiveness of topical antimicrobial preparations after safety of a substance has been assured is to apply the product to volunteer subjects. This "in vivo" procedure is an actual in-use study that can indicate how well the substance will perform in preventing microbial growth that leads to malodors.
The Induction Phase involves abstinence from particular similar substances to the test substance for a period of about three weeks. The Challenge Phase involves the application of the test substance to sites previously unexposed to the study product and noted for providing an environment conducive to microbial growth. This Challenge Phase of applying the test substance to the area daily can last from three to six weeks. Evaluation of the ability of the test substance to perform can be done by "sniffing" for malodor production of taking actual microbial counts on the test area.
It should be apparent therefore, that a need exists for a simplified and less expensive procedure for testing antimicrobial agents and topical cosmetic an pharmaceutical products containing antimicrobial agents as active ingredients.
The method according to the present invention is believed to meet this need, and is considered unique and distinct from the methods of the prior art, in that it has not heretofore been known to determine microbial characteristics in "repeat insult" testing procedures. Prior "repeat insult" testing has been limited to "in container" preservation applications, and it has not been possible to determine from such "in container" tests, the effectiveness of an antimicrobial agent on the skin. The present method is capable of indicating not only the effectiveness of an antimicrobial agent over time, but in addition, it is capable of demonstrating the efficacy of "entrapped" antimicrobial agents.